High brightness illumination modules are used in a number of lighting applications, such as ambient lighting, accent lighting, wall washing, signage, advertising, decorative and display lighting, facade lighting, custom lighting and the like. These illumination modules typically include a plurality of light sources, such as incandescent bulbs, fluorescent tubes, neon, or solid-state light-emitting diodes (LEDs), coupled to a power management system to supply and control the intensity of the light sources depending on the brightness requirements of the lighting application.
While in operation, most high brightness illumination modules generate excess amounts of thermal energy. In the case of incandescent bulbs, the thermal energy is used to heat the filament to high temperatures in order to produce light. However, for solid-state luminaries having LEDs, the thermal energy from the LEDs is transferred to the substrate, causing an increase in temperature and the LEDs to function less optimally resulting in a reduction in the luminous flux of the output light. As a result, more drive current is required to maintain the output light of the LEDs at the required level. However, increases in the drive current causes a further temperature increase in the substrate, thereby compounding the negative impact of the thermal energy on the performance of the solid-state illumination module.
Another aspect of solid-state luminaries is the need for a relatively large optic in order to provide as much mixing as possible of the different wavelengths emitted from separate light-emitting diodes within the luminaire. Another potential benefit of a large optic is the greater effectiveness of collimation of the output beam. Often the size and positioning of the thermal management system in a luminaire restricts the space available for beam shaping optics, which can reduce the quality of coloured light mixing and beam collimation.
It is therefore desirable to develop a thermal management system to overcome the undesirable effect of excess heat on the performance of solid-state illumination modules, without unduly compromising the performance of the optical system. An example of such a thermal management system is a heat pipe. A heat pipe is a thermally conductive pipe which contains a small quantity of working fluid such as water therein. Generally, one end of the heat pipe is positioned proximate to the heat source to maintain thermal contact with the heat source, for example an LED. As the temperature of the heat source increases, the thermal energy generated by the heat source causes the liquid inside the heat pipe to vaporize. As a result, heat from the heat source is absorbed by the vaporizing liquid, thereby removing heat from the heat source. The vaporized liquid travels away from the heat source, through the pipe, to the cool end of the pipe, typically referred to as the condenser end. At the condenser end of the heat pipe, the vapor condenses to its original liquid form and the heat dissipation cycle is completed. Typically, the condensing end of the heat pipe is thermally connected to a heat sink for improved heat dissipation.
A number of heat pipe thermal management systems have been proposed. United States Patent Application Publication No. 2006/0092639 to Livesay et al. describes a light source having multiple heat pipes arranged to form a light recycling cavity. Light from arrays of LEDs mounted on the heat pipes is captured and reflected from the light recycling cavity. In this set-up, the heat travels away from the source either perpendicularly to the light emitted by the source, or in the opposite direction to that of the light emitted by the source, wherein both of these configurations can result in a bulky arrangement.
United States Patent Application Publication No. 2005/0092469 to Huang teaches a loop heat pipe for cooling an LED illumination apparatus. The evaporator end of the loop heat pipe is in thermal communication with the LEDs, and the condenser end of the heat pipe is associated with a cover of the illumination apparatus. A drawback associated with the loop heat pipe of Huang is that the cover becomes bulky and has to adopt the shape of the loop heat pipe. Use of such a loop heat pipe may require a complicated arrangement which may restrict the design of the illumination apparatus and may increase costs.
United States Patent Application Publication No. 2005/0169006 to Wang et al. describes an LED lamp having a heat sink with a reflector, an LED module, and a generally U-shaped heat pipe thermally coupled at one end to the LED module and to the heat sink at the other end. In this LED lamp, the heat pipe is generally positioned opposite to the light emitting side of the light source, which may result in an elongated configuration of the LED lamp.
U.S. Pat. No. 5,852,339 to Hamilton et al. teaches a heat sink for dissipating the heat from the driver circuitry of an electrodeless bulb assembly. The heat sink of Hamilton et al, includes a number of heat pipes arranged longitudinally along the length of the heat sink. The heat sink disclosed by Hamilton et al, is designed to direct the heat away from the drive circuitry rather than the electrodeless bulb.
United States Patent Application Publication No. 2005/0258438 to Arik et al, discloses a lighting apparatus having LED chips mounted on a chip support wall that is coupled to a concave sealed volume. This sealed volume includes a heat transfer fluid and defines a passive heat pipe for cooling the LED chips. To operate effectively, the sealed volume is configured such that it is a certain minimum size. As a result, this arrangement for a lighting apparatus may not be practical due to the requirement of a larger volume as more LED chips are being used, which can result in a bulky lighting apparatus.
United States Patent Application Publication No. 2006/0196651 to Board et al, discloses an optoelectronic device which includes a light emitting semiconductor device coupled to a transparent or translucent heat pipe. The light emitted by the light emitting semiconductor device is transmitted through and along the length of the heat pipe. For this configuration of an optoelectronic device, as the heat pipe is also used for light transmission the optical efficiency of this device will be hindered the phase changes of the working fluid in addition to the multiple interfaces through which the light must pass and thus the heat pipe provides both heat transfer and light transmission. This configuration of an optoelectronic device would therefore result in a diminished luminous flux output therefrom. In addition the versatility of design of an optoelectronic device of this configuration is limited by the required configuration of the heat pipe.
U.S. Pat. No. 7,011,431 to Ono et al, provides a lighting apparatus having a light-emitting unit and a heat dissipation unit, whereby heat is transferred from the light-emitting unit to the heat dissipation unit using a heat pipe. Accordingly, the heat pipe as disclosed by Ono et al, serves only as a conduit for transfer of thermal energy, and a heat dissipation unit is still required to dissipate heat from the lighting apparatus. In addition, the lighting apparatus as proposed by Ono et al. can be complex and can include a plurality of mechanical parts, which can again lead to a bulky lighting apparatus.
U.S. Pat. No. 7,048,412 to Martin et al, teaches a lamp post with an axial heat pipe coupled to a lateral heat pipe to transfer heat away from the LED sources. The lamp post includes post facets where the LED sources are mounted. A segmented reflector is provided for guiding light from the LED sources. An axial heat pipe coupled to a lateral heat pipe is provided to transfer heat for dissipation. The lamp post as defined by Martin et al, is configured such that light and heat travel in opposite directions thereby resulting in an inefficient use of space.
Therefore there is a need for a new illumination module that can provide for adequate thermal management of light sources and light extraction from the light sources, while enabling a reduction in the overall size of the illumination module.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.